Microsoft Defender "this program is turned off" message

When Microsoft Security Essentials is installed, it turns off Defender because Essentials replaces Defender. Sometimes the Defender startup entry either does not get turned off or becomes re-enabled somewhere down the line. Simply run msconfig, go to the startup tab and uncheck the Defender entry. Sometimes you still get a warning that Defender is not running. This can be sticky.

If entry not in startup but you still get the warning these have worked for me:

Method 1:
1. Launch regedit (Win+R, type "regedit", hit return)
2. Locate the Key HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
3. Delete Value "Windows Defender"

Method 2:
Here is the thread where I found this answer.
Rename the program exe

using an elevated command prompt:
takeown /f "C:\Program Files\Windows Defender" /r /d y
icacls "C:\Program Files\Windows Defender" /grant Administrators:F /t
Yes, use the quotes or path will not be recognized.

Or use your user name instead of Administrators or  try Administrator without the s.
Now rename the file
Before (Original name):
C:\Program Files\Windows Defender\MSASCui.exe
After:
C:\Program Files\Windows Defender\aMSASCui.exe

As usual, Microsoft recommends reinstalling or restoring Windows.
The lame brains who think this is not an issue have not installed enough systems. I don't know why it happens but if you need to change the names of users or machine after initial setup may be one instance. Why is a mystery. It is one of those "Oh Crap" moments.

Forget services or gpedit, they have never worked for me on this issue.
No, uninstalling Essentials and reinstalling did not fix it.
No, turning of Defender from within Defender did not fix it.